1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus for forming an image on a long sheet.
2. Description of Related Art
In general, an electrophotographic image forming apparatus (such as a printer, a copy machine, and a fax machine) is configured to irradiate (expose) a uniformly-charged photoconductor (for example, a photoconductor drum) with (to) laser light based on image data to form an electrostatic latent image on the surface of the photoconductor. The electrostatic latent image is then visualized by supplying toner from a developing device to the photoconductor on which the electrostatic latent image is formed, whereby a toner image is formed. Further, the toner image is directly or indirectly transferred to a sheet through an intermediate transfer belt, followed by heating and pressurization for fixing, whereby an image is formed on the sheet.
When long sheets such as roll paper and continuous paper (continuous form paper) are used for image formation in the above-mentioned image forming apparatus, the long sheets stay in the sheet conveyance path during a non-image formation period such as a standby state (idling state). In particular, when a long sheet is kept sandwiched at a fixing nip during the warming-up prior to the start of an image formation or during the cooling-down after an image formation, discoloration (burn) or deformation of a long sheet is caused due to the heat directly transmitted to the long sheet. For this reason, normally, a fixing side member (for example, a fixing roller) for forming a fixing nip and a back side supporting member (for example, a pressure roller) are separated from each other.
However, since the distance between the fixing side member and the back side supporting member separated from each other is normally about 2 to 3 mm, a long sheet makes contact with the fixing side member when the long sheet is slackened. Such a problem may be solved by separating the fixing side member and the back side supporting member from each other by a great distance as necessary. In addition, it has been proposed to appropriately convey a long sheet so as not to slacken a long sheet (see, for example, PTL 1: Japanese Patent Application Laid-Open No. 2008-233770).
Furthermore, the above-mentioned problem may be solved by providing a heat insulating mechanism for blocking heat transmission from a fixing side member to a long sheet, by using highly heat-resistant long sheets, or by continuing the feeding of long sheets even during the non-image formation period.
However, when a heat insulating mechanism is provided, or when the fixing side member and the back side supporting member are separated from each other by a great distance as necessary, the size of the image forming apparatus is increased. When a heat insulating mechanism is provided, the number of components is increased, and the cost of the apparatus is also increased.
In addition, when only highly heat-resistant long sheets can be used in an apparatus, such an apparatus is not useful and cannot be used as a product. In addition, when the feeding of long sheets is continued even during the non-image formation period, the number of waste sheets (wasted sheets) is increased, which is a serious disadvantage as a product.